Cuesta College, San Luis Obispo, CA
Students have a weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.
The following questions were asked on reading textbook chapters and previewing a presentation on free fall.
Selected/edited responses are given below.
Describe what you understand from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically demonstrate your level of understanding.
"I understand the definition of free fall, and the acceleration, regardless of object mass. I also understand that no other forces act on an object other than the gravitational force."
"I understand the basic concepts and equations used in determining free fall of an object, whether it is dropped or thrown upwards."
Describe what you found confusing from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically identify the concept(s) that you do not understand.
"The highest point of the object where the velocity is zero, but doesn't stay zero because it is still traveling and then the velocity increases. That for some reason is hard for me to see and could see myself getting easily confused with that."
"The equations are overwhelming and the graphs are confusing."
Explain what assumptions are made about the amount of drag (air resistance) on an object said to be in free fall.
"There is always some air resistance so it is said that free fall on Earth is an idealization, but since air resistance is so small it is assumed to be negligible."
"Air resistance is assumed to be negligible when measuring velocities of free-falling objects that aren't falling very fast."
For all possible cases of an object during free fall, ay =
+9.80 m/s2. *************** [15] 0. [0] -9.80 m/s2. ************************************ [36] (More than one of the above choices.) *** [3] (Unsure/guessing/lost/help!) **** [4]
For all possible cases of an object during free fall, the distance traveled will be __________ to the magnitude of the displacement.
less than. ****** [6] equal to. ************************* [25] greater than. *********** [11] (More than one of the above choices.) *********** [11] (Unsure/guessing/lost/help!) ***** [5]
For all possible cases of an object during free fall, the magnitude of the average acceleration will be __________ to the magnitude of the instantaneous acceleration.
less than. ********* [9] equal to. ******************************* [31] greater than. ***** [5] (More than one of the above choices.) ***** [5] (Unsure/guessing/lost/help!) ******** [8]
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"This section kind of made my head hurt."
"What do you mean when you say, 'for all possible cases of an object during free fall?'" ("Free fall" means no forces other than gravity (i.e., negligible drag), and it doesn't matter whether the object is moving upwards, downwards, or is momentarily at the top of its trajectory.)
"How do you know if the vertical acceleration ay has a positive or negative sign in front of 9.80 m/s2?" (ay is always -9.80 m/s2 in free fall (assuming that up is the +y direction). And that value is still negative whether the object is moving upwards, downwards, or is momentarily at the top of its trajectory.)
"If an object is thrown down, is the force of the throw added to the acceleration? Would throwing an item or dropping it not count as a free fall?" (While the object is being thrown (still in contact with your hand), the force of your throw must be included. However, the object will only be in free fall after you let go (whether with an initial upwards or downwards velocity, or released from rest), as then gravity is the only force acting on it from that point onwards.)
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